Frictional composition



Patented Mar. 8, 1938 UNITED STATES PATENT OFFICE No Drawing. Application A pril 20, 1936, Serial No. 75,507

4 Claims.

This invention relates to compositions for friction members, such as are used as brake, clutch or similar linings. The composition herein described is not limited to any particular use, but may be used wherever a frictional member is desired for any purpose.

A general object, of the invention is to provide a frictional composition having a frictional coefiicient as high or as low as may be desirable, having a smooth and non-abrasive action, having an action which is little influenced by the varying temperatures ,under which such a composition must operate, or by becoming wetted; and having the advantages of cheapness, and simplicity of preparation and formation, and also long life. In the accomplishment of these and other objects, my frictional composition embodies essentially a composite structure made up of a finely divided soft metal, such as finely divided lead or other 1 similar soft metals as hereinafter indicated, held in. a matrix or binder of suitable material or materials, so that the finely divided metal particles are sufiiciently and properly supported in a body having sufficient strength and rigidity, and so that the fine metal particles are held separately and spacedly from each other.

The metal or metals selected for use in the composition may be one or more of several different metals having soft, frictional and non-abrasive qualities; and the matrix or body of the. composition may be made up of one or more materials selected from a larger member having the desired qualities.

The invention will be best understood from the following more specific description, which sets Solids: Percent and. preferably less.

Of the total liquids, the amounts given are those to be used for each 22 pounds of the total of solids used. The percentages given in the right hand column are the approximate percentages by weight of each ingredient in the final product. From the foregoing example, it will be seen that the composition contemplated by this invention is composed substantially entirely of finely divided soft metal particles. In this particular example, it will be observed that,the main body of the composition is made up of 41.95 percent powdered lead and the same amount by weight of powdered zinc, making the total content of powdered metal in the neighborhood of 84 percent. As will be hereinafter noted, however, the amount of metal and the proportions of the metals with respect to each other may be varied, also other soft metals than those specified above may be used, but in any event, it is important to the obtainment of the results contemplated by this invention that the main body of the composition be composed substantially entirely of this powdered metal, which is held in a compressed matrix of suitable binding material, the other ingredients going mainly to varying the co-efficient of friction and other characteristics of the compound, depending upon the use to which it is to be applied.

The proportions; of the above ingredients, and the ingredients themselves, may be varied, substituted or omitted, to make compositions of varying characters for" different uses, as will appear hereinafter. The foregoing formula is typical.

The preparation of the materials, and the preparation of the composition from the materials is typically as follows. First, it must be seen that all of the powdered materials are substantially completely dry, and that there are no lumps of particules or particles adhering to each other. For this purpose I find it best to rescreen the powdered materials after mixing them together and after heating them. to a temperature of approximately 150 F., using a screen of 200 mesh. The gilsonite is not included in this heating and drying, but is heated and dried under a lower temperature so as not to soften it; just enough heat being usedv to dryit. The asbestos is rather coarse, compared to the other materials, and is also heated, dried and screened separately.

' The powdered dry materials are then all mixed together, and then mixed with the liquids which have been previously mixed together; the final mixing of the liquids and powders being done When the powders are cold. This mixing produces a wet mass which, when somewhat dried, can be molded into any desired form.

But the preferred procedure is first to dry and then pulverize the mixed mass, using a drying temperature of not over approximately 150 F.,

The result is again a substantially dry powder which is then screened through a comparatively coarser screen, say a 16 mesh screen, and is then molded.

Whether the molding is done immediately from the Wet mixed mass, or from the repulverized and dried materials, it is accomplished under the suitable heat and pressure which is used for bakelite molding. I find a temperature of about 305 F. to be suitable. A suitable pressure I find to be about 10,000 lbs. per sq. inch.

The general physical nature of the finished product may be best described as a distribution of the finely divided soft metal particles in a cellular matrix which is formed of the other ingredients. The bakelite forms the essential binder for the remaining ingredients; and therefore the solidified bakelite may be looked upon as the binder which forms the matrix of the cellular mass in which the metal particles are spacedly dispersed and held, along with the dispersed particles of the other materials. Or the bakelite, together with the other materials aside from the soft metal, imbedded in it, may be looked upon as the binder matrix of the composition, in which the dispersed metal particles are held.

The ofiice and purpose of. the bakelite is substantially solely that of acting as the binder, forming a cellular body which imbeds and encases the remaining particles. Other suitable materials may be used'as a substitute for the bakelite; for instance, such materials as silica, casein, or cement of various kinds including Portland cement, may be used. However, in my work thus far I have found bakelite to be the most conveniently usable of such binder materials, and italso gives a very satisfactory performance. It will be understood of course that the alcohol and benzol, which are used merely for thinning out the liquid bakelite to obtain an even distribution of it throughout the mass, are evaporated during the heating and drying before or during molding. And one of the reasons for my preference for first drying and pulverizing the wet mass before final molding, is that such preliminary drying drives off certain gases that otherwise will be driven off during the heated molding, or eventually driven off when the composition is heated in use.

The lead and zinc, which are above given as preferred soft metals for the composition, may be substituted by any suitable soft metal. Thus for instance I may usesuch metals as copper, antimony, soft pure iron; in fact any relatively soft metal will do. Some of such metals are of course more suitable than others, due to differences in cost, ease of division, tendency to oxidize or deteriorate under heat, etc. For various such reasons I find that either lead or zinc is a suitable metal; and I find that the mixture of the two has certain advantages. The lead has a somewhat greater friction co-efiicient than the zinc, and'the zinc has a higher melting temperature than the lead; and consequently a composition utilizing particles of both these metals has to a certain extent the desirable frictional quality of the lead and also the desirable heat resistance of the zinc.

The composition can be made, using the bakelite or other substitute binder alone with the,

iceability at higher temperatures) and act as reinforcements to the bakelite. The asbestos to a certain extent also increases the heat resistance and acts as a fibrous reinforcement; but its main purpose of use in this composition is to displace a corresponding amount of other materials such as graphite, carbon, and iron oxide which are more expensive. and thus to make a somewhat cheaper but still satisfactory composition.

The gilsonite (a. hydrocarbon somewhat like coal or asphalt, found in nature) is used mainly as an element to increase the frictional coefficient, and can be omitted.

The graphite also acts as a lubricant, aiding in obtaining smooth frictional action.

The finished molded composition, when put to use as a frictional element does not bleed out any of its ingredients under any reasonable operating'heat. The soft metals, finely divided and separated in fine particles, may soften or even melt to a certain extent at the friction surface; but as they are prevented from running together there is no appreciable tendency for any liquid metal to run out or be dragged out of the mass.

Temperature changes, high 'or low, within any ordinary ranges do not affect the frictional action or disintegrate the material; and water does not affect it to any appreciable degree, as water cannot readily penetrate the mass and the first application of the friction surface under pressure squeezes out any surface film. The composition is similarly non-absorbent of oils and greases, and is not affected by them. The friction coefficient of the composition slightly increases with increases of temperature up to the highest operative temperature. The finished product has a smooth, non-abrasive action, and will not develop squeaks. It wears particularly well. And it stands up under extremely heavy physical stresses, such as are imposed in heavy braking service.

I have given an idea of the substitutions and omissions that may be practised. The following will give an idea of the variations in proportion that may be used.

Using all the ingredients given above, the composition may be further cheapened by increasing the proportion of asbestos with a corresponding decrease of metal. The other ingredients could of course also be increased in amounts along with the asbestos, but there is no apparent good reason for doing so except to proportionately increase their individual actions.

If the asbestos is decreased in amount or eliminated entirely, the remaining ingredients can remain at the same amounts as given, .or the metal content can be increased.

The proportionate amount of bakelite or other binder may be varied. It may be somewhat decreased in proportion to the metal or all the other ingredients, the limit being reached only when the binder amount is too small to thoroughly encase the particles of other materials. And of course the binder proportion may be increased at the expense of the proportion of metal or other ingredients. Such increase merely increases the thickness of the cellular binder matrix in which the particles are held.

The other four ingredients may be varied in amounts as desired to obtain more or less of their individual qualities in the final product.

I claim:

1. A frictional composition comprising finely divided particles of soft metal spacedly held Within a cellular matrix made up of a solidified binder and iron oxide and carbon said soft metal particles constituting more than fifty percent by weight of the entire composition.

2. A frictional composition comprising finely divided particles of soft metal spacedly held Within a cellular matrix made up of a solidified binder and iron oxide, carbon and asbestos said soft metal particles constituting more than fifty percent by weight of the entire composition.

3. A frictional composition comprising finely divided particles of a soft metal spacedly held in a cellular matrix composed of solidified bakelite and interspersed and finely divided iron oxide, carbon black, gilsonite, graphite, and asbestos said soft metal particles constituting more than fifty percent by Weight of the entire composition.

4. A friction composition composed substantially entirely of a mixture of powdered lead and zinc, said powdered metal being substantially uniformly distributed throughout a compressed matrix of binding material.

ARTHUR F. ELERATH. 

